In a silver halide photographic element, a color image is formed when the element is exposed to light and then subjected to color development with a primary aromatic amine developer. Color development results in imagewise reduction of silver halide and production of oxidized developer. Oxidized developer reacts with one or more incorporated dye-forming couplers to form an imagewise distribution of dye.
The dyes that are formed by any color coupler during processing have a tendency to fade over time as a result of exposure to light, heat, humidity and oxygen. As all three image dyes of a typical color element fade, this results in overall fading of the image over time. In addition, since the three image dyes may not fade at the same rate, an apparent change in image color may result. Such change is particularly noticeable in the case of magenta image dye fading.
A significant disadvantage of many magenta dye-forming couplers is fading of the dyes formed from them by photographic processing due to extended exposure to low levels of light. Compounds which are included in photographic elements to reduce image dye fading are known as stabilizers. Inclusion of stabilizers in color photographic materials can reduce the deterioration of the dye images which occurs over time as a result of the action of light, heat, humidity and/or oxygen. This is especially true for dyes formed from pyrazoloazole couplers. U.S. Pat. Nos. 5,236,819, 5,082,766 and 5,017,465 and German Published Patent Application DTOS 4,307,194, e.g., describe the use of certain stabilizers with pyrazoloazole couplers to improve their dye stability. One class of stabilizers which is disclosed includes compounds of the following structure: ##STR2## wherein A represents a group of non-metal atoms necessary to complete a 5-membered to 8-membered nitrogen-containing ring and R.sup.0 represents an aryl group or a heterocyclic group. Preferred compounds of such formula as described in U.S. Pat. No. 5,017,465 include compounds wherein A represents the atoms necessary to complete a thiomorpholine 1,1-dioxide group and where R.sup.0 represents an alkoxy substituted phenyl group. Such compounds are believed to stabilize by acting as singlet oxygen quenchers.
It would be desirable to improve the light stability of dyes derived from magenta dye forming couplers, and thus retain the color rendition of the image for a longer period of time. It would also be desirable to provide singlet oxygen quenching stabilizers with greater structural flexibility than the prior art stabilizers comprising nitrogen-containing ring structures, so that other properties of such compounds may be more easily adjusted where desired (e.g., compound solubility and dispersibility).